As energy costs increase and the use of electric lighting, heating and motors expands, more and more attention is being given to the design of efficient electrical systems. SCR (Silicon Controlled Rectifier) and Triac-based AC (alternating current) voltage controllers have long been in use for controlling resistive loads (i.e. loads in which there is no phase difference between the voltage and current). There are also systems which have been proposed for controlling the AC power supply to fluorescent lights. For example, U.S. Pat. No. 4,287,455 (Drieu) issued on 1 Sep., 1981, discloses a control circuit which supplies current to one or more gaseous discharge lamps during an adjustable final portion of each half-cycle of the AC power supply. However, since this circuitry allows current to pass through the load only during the final portion of each half-cycle of the AC power supply, an inductive effect is produced, i.e. a time lag is created between the peak line voltage and the peak line current.
This inductive effect affects the power factor, i.e. the ratio of the power actually used by the load to the power supplied by the line, where the power is the integral of V.multidot.I.multidot.dt. In the case of a simple sinusoidal line voltage signal, the power factor may be expressed as: ##EQU1## where V and I are the voltage and current supplied by the line, and .theta. is the phase angle between the line voltage and the load current. When the line voltage and the load current are in phase, as is the case with a resistive load, cos .theta.=1, resulting in a unity power factor. But in the case of an inductive load, or a circuit which produces an inductive effect, such as a fluorescent lamp circuit, the line voltage and load current are out of phase, so cos .theta.&lt;1, resulting in a power factor having a value less than unity. Since utility companies generally charge commercial users a higher rate if the power factor falls below a particular value (e.g. 0.90), the reduction in power consumption occasioned by the use of prior art power saving circuits may in some cases be offset by the higher rate charged by the utility company.